JP2003041182A - Epoxy resin powder coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epoxy resin powder coating composition having excellent storage stability under high temperature and humidity condition and excellent adhesivity, flexibility, heat-resistance, etc. SOLUTION: The epoxy resin powder coating composition contains (A) an epoxy resin and (B) a curing agent as essential components. The curing agent used as an essential component is a polycarboxylic acid trimellitate expressed by formula 1 [R is a 2-30C triol residue having 2-4 hydroxy groups; (n) is an integer of 1-3; X and Y are each H or carboxylic acid group and are different from each other; and X' and Y' are each H or carboxylic acid group and are different from each other].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epoxy resin-based powder coating material, and particularly to an epoxy resin-based powder coating material having excellent storage stability at high temperature and high humidity, and at the same time, excellent adhesiveness, flexibility and heat resistance. The present invention relates to a powder coating composition.

[0002]

2. Description of the Related Art Among epoxy resin powder coatings, those using an acid anhydride as a curing agent have good heat resistance,
Due to its high reliability in electrical characteristics, it is widely used as an insulating coating material for electrical and electronic parts.

Particularly, an epoxy resin powder coating using trimellitic acid anhydride as a curing agent component is
It is known to have excellent heat resistance and flexibility. (JP-A-51-116900, JP-A-57-84)
843, JP-A-7-62293, etc.).

However, the epoxy resin-based powder coating material using such an acid anhydride has poor storage stability, and when the obtained powder coating material is left to stand, it gradually gels to give a desired coating film. It has the drawback that it cannot be obtained or the powder coating itself blocks. In order to improve this, the trimellitic acid ester anhydride is refined to be highly purified (JP-A-2-240074) or crystallized to improve the storage stability (JP-A-8-2393).
No. 76) has been proposed, but there is room for further improvement in storage stability under high temperature and high humidity conditions.

On the other hand, in epoxy resin powder coatings using aliphatic polycarboxylic acids such as dodecanedioic acid,
Although such powder coatings using an acid anhydride do not deteriorate in storage stability, the overall performance as a curing agent is inferior to that of trimellitic acid ester anhydride, such as the heat resistance is greatly inferior.

Further, when the trimellitic acid ester anhydride is used as a polycarboxylic acid by ring-opening with water as it is, the storage stability of the epoxy resin-based powder coating material becomes good, but when it is cured. In addition, there is a problem that the polycarboxylic acid undergoes thermal ring closure again, and the cured product foams due to water generated at that time, which is not practical.

[0007]

DISCLOSURE OF THE INVENTION The present invention has various coating film physical properties such as adhesiveness, flexibility and heat resistance, which are comparable to epoxy resin powder coatings using an acid anhydride as a curing agent, and It is an object of the present invention to provide a novel epoxy resin-based powder coating composition having remarkably improved storage stability.

[0008]

Means for Solving the Problems As a result of intensive studies to achieve the above objects, the present inventors have found that an epoxy resin powder coating composition using a specific trimellitic acid ester polycarboxylic acid as a curing agent is It has been found that it has excellent storage stability at high temperature and high humidity, and at the same time, it also satisfies performances such as adhesiveness, flexibility, and heat resistance, and based on such findings, the present invention has been completed.

That is, the epoxy resin powder coating composition of the present invention is an epoxy resin powder coating composition containing (A) epoxy resin and (B) curing agent as essential components,
The general formula (1) as the curing agent (B) [In the formula, R is 2 to 30 carbon atoms having 2 to 4 hydroxyl groups.
Represents a polyol residue of. n represents an integer of 1 to 3. X
And Y represent a hydrogen atom or a carboxylic acid group, and X and Y are always different. X'and Y'represent a hydrogen atom or a carboxylic acid group, and X'and Y'are always different. ] It is characterized by containing the trimellitic acid ester polycarboxylic acid represented by these as an essential component.

The compounding amount of the trimellitic acid ester polycarboxylic acid represented by the general formula (1) is 50% by weight or more of the curing agent (B).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION (B) of the epoxy resin powder coating composition of the present invention (hereinafter referred to as "powder coating composition").
The trimellitic acid ester polycarboxylic acid (hereinafter, referred to as “present polycarboxylic acid”) represented by the general formula (1), which is mixed as a curing agent, is a reaction intermediate in the process for producing a trimellitic acid anhydride. Yes, obtained by addition reaction of trimellitic anhydride and polyol (Japanese Patent Publication No.
5-29974). This polycarboxylic acid, which is this reaction intermediate, can be obtained by isolation and purification by a known method such as the method described in JP-A-53-82743. Specifically, trimellitic anhydride and the general formula (2) [In the formula, R and n have the same meanings as defined in the general formula (1). ] The polyol having 2 to 4 hydroxyl groups in the molecule represented by the above is subjected to an addition reaction in a good solvent such as cyclohexanone or γ-butyrolactone at 70 to 120 ° C for 1 to 12 hours, and then toluene or xylene or the like. The polycarboxylic acid can be obtained by precipitating the adduct in a poor solvent, filtering and drying. The addition reaction may be carried out without catalyst or in the presence of a catalyst.

The polyol represented by the general formula (2) is 2
It is a C3-C30 chain aliphatic polyol, alicyclic polyol, or aromatic polyol having a valence of 3, a valence of 3 or a valence of 4.
Of these, a polyol having a hydroxyl group at the terminal is preferable.

Specifically, ethylene glycol, 1, 2
-Propanediol, 1,3-propanediol, 1,
4-butanediol, 1,5-pentanediol, 3-
Methyl 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, neopentyl glycol, methylpropylpropane Aliphatic diols such as diols, cyclohexanediol, hydrogenated bisphenol A, hydrogenated bisphenol F, hydrogenated bisphenol Z, cyclohexanedimethanol, and alicyclic diols such as alkylene oxide adducts (addition mole number 2 to 4) thereof, p-xylylene-
Aromatic diols such as α, α'-diols, hydroquinone, bisphenol A, bisphenol F, bisphenol Z and their alkylene oxide adducts (addition mole number 2 to 4), diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, etc. Examples thereof include glycol ethers and the like. Further, glycerin having 3 or 4 hydroxyl groups, trimethylolpropane, pentaerythritol and the like can also be used.

Among these, ethylene glycol, 1,2-propanediol,
1,4-butanediol, 3-methyl-1,5-propanediol, 1,6-hexanediol, bisphenol A are recommended. Further, ethylene glycol, 1,4-butanediol, and 1,6-hexanediol are particularly recommended in terms of good heat resistance and flexibility of the powder coating composition.

The present polycarboxylic acid is a crystal powder having a purity of 50% or more, preferably 70% or more, and the maximum particle size thereof is 1 mm or less, preferably 600 μm or less, more preferably 180 μm or less. Further, they can be used by pulverizing and classifying as needed.

The present polycarboxylic acid can be used alone or as a mixture of two or more kinds.

As the curing agent (B) of the powder coating composition of the present invention, a carboxylic acid other than the polycarboxylic acid of the present invention or an anhydride thereof can be used in combination, if necessary. At this time, the present polycarboxylic acid is preferably added in an amount of 50% by weight or more, more preferably 70% by weight or more, of the curing agent (B) as its pure content.

Examples of the carboxylic acids or their anhydrides that can be used in combination include dibasic acids such as phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, methyltetrahydrophthalic acid, methylhexahydrophthalic acid, nadic acid and methylnadic acid, and the like. Structural isomers or stereoisomers and their anhydrides, trimellitic acid, pyromellitic acid, benzophenonetetracarboxylic acid, trifunctional or more carboxylic acids such as biphenyltetracarboxylic acid and anhydrides thereof, etc., and conventional powder What is known as a hardening agent for paints can be used.

The epoxy resin (A) used in the powder coating composition of the present invention includes bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin. Resins, alicyclic epoxy resins, hydrogenated bisphenol A type epoxy resins, hydrogenated bisphenol AD type epoxy resins, aliphatic epoxy resins such as propylene glycol diglycidyl ether, pentaerythritol polyglycidyl ether, aliphatic or aromatic carboxylic acids Among various epoxy resins such as epoxy resin consisting of and epichlorohydrin, heterocyclic epoxy resin, spiro ring-containing epoxy resin, epoxy group-containing acrylic resin and epoxy modified resin, the epoxy resin which is solid at room temperature is It is shown. These epoxy resins are used alone or in appropriate combination of two or more kinds.

Particularly recommended epoxy resins include bisphenol A type epoxy resins having an epoxy equivalent of 450 to 4000, which are available from Japan Epoxy Resins Co., Ltd.
Epicoat 1001, Epicoat 1002, Epicoat 1003, Epicoat 1004, Epicoat 1007,
It is marketed under the trade name of Epicote 1009 and the like.

It is also possible to use an epoxy resin which is liquid at room temperature in combination within a range that does not cause blocking.

The content of the (B) curing agent in the powder coating composition of the present invention is such that the ratio of the carboxyl group of the (B) curing agent to one epoxy group of the (A) epoxy resin used is [carboxyl group / Epoxy group equivalent ratio] is 0.2
The amount is preferably in the range of 1.2 to 2.
5 is recommended. If it is less than 0.2, it is difficult to obtain good coating properties such as insufficient heat resistance, and if it exceeds 4.0, it becomes difficult to mix the (A) epoxy resin and the (B) curing agent. However, in any case, it is not preferable.

In the powder coating composition of the present invention, a curing accelerator is optionally added to 0.01 to 5 parts by weight, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the epoxy resin (A). Parts can be compounded. By blending 0.01 part by weight or more of the curing accelerator, the curing condition can be lower temperature and shorter time. Further, in order not to impair the storage stability of the powder coating composition, it is preferable to limit the content to 5 parts by weight.

As such a curing accelerator, conventionally known curing accelerators, for example, tertiary amines such as triethylamine, N, N-dimethylbenzylamine, N, N-dimethylaniline and tris (dimethylaminomethyl) phenol, 2-undecylimidazole, 2-heptadecylimidazole, imidazoles such as 1-cyanoethyl-2-undecylimidazole, quaternary ammonium salts such as tetraethylammonium bromide, tetrabutylammonium bromide, zinc acetate, sodium acetate, Examples thereof include organic metal compounds such as zinc octylate, tin octylate and aluminum acetylacetone, and organic phosphorus compounds such as triphenylphosphine and triphenylphosphite.

Further, in the powder coating composition of the present invention, if necessary, an ultraviolet absorber, an antioxidant, a light stabilizer, a pigment, a dye, a filler, a flame retardant, a flow regulator, a leveling agent, a surface. Other additives such as a tension adjusting agent, a tackifier, a coupling agent, an antifoaming agent and the like can be appropriately added within a range that does not impair the effects of the present invention.

The powder coating composition of the present invention comprises (A) an epoxy resin, (B) a curing agent, and, if necessary, a curing accelerator and other additives, which are mixed and melted using a conventionally known apparatus. It is prepared by kneading and pulverizing. Specifically, these ingredients are dry-mixed using a Henschel mixer or the like, and then melt-mixed at a temperature of, for example, 90 ° C. to 130 ° C. by a kneader, an extruder or the like, and then the mixture is cooled and solidified, Crush and classify. The particle size of the powder coating composition of the present invention is such that the maximum particle size is usually 1000μ.
m or less, preferably 150 μm or less.

The powder coating composition thus obtained is remarkably excellent in storage stability and further has various cured coating physical properties such as adhesiveness, flexibility and heat resistance in a well-balanced manner. Electronic components such as varistor and hybrid IC, transformer,
Power components such as bus bars, prefabricated steel frames, gates, fences, civil engineering materials such as sashes, steel furniture such as desks and lockers, refrigerators, washing machines, microwave ovens, household electrical appliances such as lighting equipment, transportation It is useful as a paint for traffic related products such as signs and guardrails, vehicle related products such as automobiles and motorcycles, pipes such as gas pipes and water pipes, and cans.

The powder coating composition of the present invention can be prepared by a known method,
For example, fluidized immersion method, electrostatic fluidized immersion method, electrostatic spraying method,
It is applied by various coating methods such as sprinkling method, rolling method, thermal spraying method, and fog box method. The baking conditions are usually 100 ° C. or higher, preferably 120 to 250 ° C.

[0029]

EXAMPLES The present invention will be described in detail below with reference to examples. The methods for measuring various physical properties of the powder coating composition in each example are as follows.

[Storage stability of powder coating composition] The storage stability of the powder coating composition is determined by the glass transition temperature ratio, gel time ratio, heating horizontal flow rate ratio, powder coating blocking resistance,
Evaluation was made by measuring the blisters of the cured product and the strength of the cured product.

[Heating Horizontal Flow Rate] Powder coating composition 0.6
g is treated with a pressure granulator (RIKEN POWER MODEL P-18, manufactured by Riken Seiki Co., Ltd.) at 60 kg / cm ² for 1 minute to give tablets with a diameter of 1 cm. Use this tablet as a standard tin plate (JI
S G-3303) is placed in the center, placed horizontally in an oven at 180 ° C., and heat-cured for 30 minutes. The diameter of the tablets after being taken out is measured, and the rate of increase in diameter [diameter after hardening /
The diameter before heating × 100 (%)] was defined as the horizontal flow rate under heating.

[Heating Horizontal Flow Rate Ratio] The heating horizontal flow rate (T0) immediately after the production of the powder coating composition and the powder coating composition were stored for 30 days in an atmosphere of a temperature of 35 ° C. and a relative humidity of 90%. After heating, the horizontal flow rate (T1) was measured and expressed as the ratio of T0 and T1 (T1 / T0). Number is 1.0
The closer to, the better the storage stability.

[Glass Transition Temperature] A powder coating composition as a sample was granulated and cured according to the method for measuring the horizontal flow rate under heating, and the cured product was used to prepare a Shimadzu heat flux differential scanning calorimeter (DSC-). 50) under a nitrogen stream at a temperature rising condition of 20 ° C./min.

[Glass transition temperature ratio] The glass transition temperature (T0) immediately after the production of the powder coating composition and the powder coating composition were stored at a temperature of 35 ° C. and a relative humidity of 90% for 30 days. The subsequent glass transition temperature (T1) was measured and expressed as the ratio of T0 and T1 (T1 / T0). Number is 1.0
The closer to, the better the storage stability.

[Gel time] In accordance with JIS C-2104, 0.1 g of the powder coating composition as a sample was put into the circular recess of the hot plate kept at 180 ° C., and the time until the powder coating gelled (second) ) Was measured.

[Gel time ratio] The gel time (T0) immediately after the production of the powder coating composition and the gel time after the powder coating composition was stored for 30 days in an atmosphere of a temperature of 35 ° C. and a relative humidity of 90% ( T1) was measured and expressed as a ratio of T0 and T1 (T1 / T0). The closer the value is to 1.0, the better the storage stability.

[Blocking resistance of powder coating material] 20 g of a powder coating material composition as a sample was put in a petri dish (diameter 55 mm x depth 30 mm), the temperature was 35 ° C and the relative humidity was 90 without a lid.
%, And the period (days) until blocking occurred was measured. Blocking was judged visually and by touching with a finger. The longer the period, the better the storage stability.

[Bubbling of Cured Product] 20 g of a powder coating composition as a sample was put in a petri dish (diameter 55 mm × depth 30 mm), and left in an atmosphere of a temperature of 35 ° C. and a relative humidity of 90% without a lid. Initially (before standing), after 1 day of standing, after 15 days of standing, and after 30 days of standing, they were granulated and cured according to the measurement of the horizontal flow rate of heating, and the presence or absence of foaming of the cured product was visually determined. The judgment results are indicated by ◯: no foaming and ×: severe foaming. The longer the period of ○ is, the better the storage stability.

[Strength of Cured Product] 20 g of the powder coating composition was placed in a petri dish (diameter 55 mm × depth 30 mm) and left uncovered under an atmosphere of temperature 35 ° C./relative humidity 90%, and the initial ( Before leaving), after leaving for 1 day, after leaving for 15 days, and after leaving for 30 days, granulate and cure according to the measurement of the horizontal flow rate under heating, and the strength (brittleness) when the cured product is forcibly divided in half by pliers. The strength was evaluated by the feeling of (adjustment). The evaluation results were expressed in three grades: ◯: good strength, Δ: slightly brittle, x: very brittle. The longer the period of ○ is, the better the storage stability.

Production Example 1 267.0 g (1.4 mol) of trimellitic anhydride, 43.4 g (0.7 mol) of ethylene glycol, N, N- were placed in a 1 liter reaction vessel equipped with a thermometer and a stirrer. Dimethylbenzylamine 0.57 g (0.0042 mol), γ
-Butyrolactone 234.3 g and xylene 234.3
g was charged and reacted at 100 ° C. for 3 hours. As the reaction proceeded, the reaction product gradually precipitated as white crystals. After the reaction, the crystallized product was cooled to 40 ° C. and filtered off, rinsed thoroughly with xylene, and dried in a vacuum dryer to obtain 240.4 g (yield 70.6%) of a white powdery crystal product. The acid value of this product is 504.6 (theoretical value 503.2), the ester value is 250.8 (theoretical value 251.4), and the IR spectrum shows that the product has the following structure: It was confirmed to be a meritic acid ester tetracarboxylic acid (hereinafter referred to as "EGBT"). [Wherein, X and Y represent a hydrogen atom or a carboxylic acid group,
X and Y are always different. X'and Y'represent a hydrogen atom or a carboxylic acid group, and X'and Y'are always different. ]

Production Example 2 Trimellitic anhydride 267.
0 g (1.4 mol), 1,4-butanediol 63.1
g (0.7 mol), cyclohexanone 247.6 g and xylene 247.6 g were charged and reacted at 100 ° C. for 3 hours. As the reaction proceeded, the reaction product gradually precipitated as white crystals. After the reaction, the crystal product was cooled to 40 ° C. and filtered off, thoroughly rinsed with xylene, and then dried with a vacuum dryer to obtain 298.4 g of a white powder crystal product (yield 90.4).
%) Was obtained. The acid value of this product was 467.6 (theoretical value 47).
3.5), ester value 239.8 (theoretical value 236.
6), the IR spectrum and the like confirmed that this product was a trimellitic acid ester tetracarboxylic acid (hereinafter referred to as “BDBT”) having the following structure. [Wherein, X and Y represent a hydrogen atom or a carboxylic acid group,
X and Y are always different. X'and Y'represent a hydrogen atom or a carboxylic acid group, and X'and Y'are always different. ]

Production Example 3 In the same apparatus as in Production Example 1, trimellitic anhydride 267.
0 g (1.4 mol), 1,6-hexanediol 82.
7 g (0.7 mol), 262.3 g of cyclohexanone and 262.3 g of xylene are charged and reacted at 100 ° C. for 2 hours. As the reaction proceeds, the reaction product gradually precipitates as white crystals. After the reaction, the mixture is cooled to 40 ° C and filtered. The crystallized product was thoroughly rinsed with xylene and then dried in a vacuum dryer to give 174.9 g of a white powdery crystal product (yield 50.
0%). The acid value of this product is 442.6 (theoretical value 4
47.1), ester value 220.4 (theoretical value 223.
4), IR spectrum and the like confirmed that this product was a trimellitic acid ester tetracarboxylic acid (hereinafter referred to as “HDBT”) having the following structure. [Wherein, X and Y represent a hydrogen atom or a carboxylic acid group,
X and Y are always different. X'and Y'represent a hydrogen atom or a carboxylic acid group, and X'and Y'are always different. ]

Example 1 100 g of bisphenol A type epoxy resin (trade name "Epicoat 1004", manufactured by Japan Epoxy Resins Co., Ltd.),
20 g of EGBT obtained in Production Example 1 and flow regulator 1.
5 g (trade name "Modaflow powder 3", manufactured by Monsanto) is melt-kneaded in an extruder at 120 ° C,
After cooling, it was pulverized with a pulverizer (trade name “small pulverizer SK-M”, manufactured by Kyoritsu Riko Co., Ltd.), and then classified with a wire net of 150 μm to obtain a powder coating composition. Glass transition temperature ratio of the obtained powder coating composition, gel time ratio, heating horizontal flow rate ratio,
Table 1 shows the measurement results of the blocking resistance of the powder coating material, the foaming of the cured product, and the strength of the cured product.

Example 2 A powder coating composition was obtained in the same amount and operation as in Example 1, except that 20 g of BDBT obtained in Production Example 2 was used instead of 20 g of EGBT as the curing agent component. Glass transition temperature ratio of the obtained powder coating composition, gel time ratio, heating horizontal flow rate ratio, blocking resistance of powder coating, foaming of cured product,
The results of measuring the strength of the cured product are shown in Table 1.

Example 3 A powder coating composition was obtained in the same amount and operation as in Example 1, except that 20 g of HDBT obtained in Production Example 3 was used instead of 20 g of EGBT as the curing agent component. Glass transition temperature ratio of the obtained powder coating composition, gel time ratio, heating horizontal flow rate ratio, blocking resistance of powder coating, foaming of cured product,
The results of measuring the strength of the cured product are shown in Table 1.

Comparative Example 1 The same charge amount as in Example 1 except that 20 g of trimellitic acid ester anhydride (hereinafter referred to as "TMEG") having the following structure was used in place of 20 g of EGBT as the curing agent component. A powder coating composition was prepared by the operation. Table 1 shows the measurement results of the glass transition temperature ratio, gel time ratio, heating horizontal flow rate ratio, blocking resistance of the powder coating material, foaming of the cured product, and strength of the cured product of the obtained powder coating composition.

COMPARATIVE EXAMPLE 2 A trimellitic acid ester tetracarboxylic acid having the following structure was used in place of 20 g of EGBT as the curing agent component (TMEG-free hydroxyl group was opened with water. Hereinafter referred to as "TMEG-W"). A powder coating composition was prepared in the same amount and operation as in Example 1, except that 20 g was used. Table 1 shows the measurement results of the glass transition temperature ratio, gel time ratio, heating horizontal flow rate ratio, blocking resistance of the powder coating material, foaming of the cured product, and strength of the cured product of the obtained powder coating composition.

Comparative Example 3 A powder coating composition was prepared in the same manner as in Example 1 except that 20 g of dodecanedioic acid having the following structure was used in place of 20 g of EGBT as the curing agent component. Table 1 shows the measurement results of the glass transition temperature ratio, gel time ratio, heating horizontal flow rate ratio, blocking resistance of the powder coating material, foaming of the cured product, and strength of the cured product of the obtained powder coating composition.

[0049]

[Table 1]

As is clear from Table 1, the epoxy resin-based powder coating composition of the present invention is a comparative example 1 using TMEG.
Compared with, the storage stability at high temperature and high humidity is significantly improved. Further, compared to Comparative Example 2 using TMEG-W having a structure in which trimellitic acid ester anhydride is simply made water-free, there is no inconvenience of foaming at the time of curing, and it also has a well-balanced cured physical property.

[0051]

EFFECTS OF THE INVENTION According to the present invention, acid anhydrides can be obtained without impairing various good cured physical properties peculiar to epoxy powder coatings using conventional acid anhydride curing agents such as adhesiveness, flexibility and heat resistance. It is possible to remarkably improve the poor storage stability at high temperature and high humidity, which is a major drawback of the epoxy powder coating composition using a material curing agent, and to obtain an excellent epoxy powder coating composition.

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Claims (2)

[Claims] 1. An epoxy resin-based powder coating composition comprising (A) an epoxy resin and (B) a curing agent as essential components, wherein the general formula (1) is used as the (B) curing agent. [In the formula, R is 2 to 30 carbon atoms having 2 to 4 hydroxyl groups.
Represents a polyol residue of. n represents an integer of 1 to 3. X
And Y represent a hydrogen atom or a carboxylic acid group, and X and Y are always different. X'and Y'represent a hydrogen atom or a carboxylic acid group, and X'and Y'are always different. ] The epoxy resin type powder coating composition containing the trimellitic acid ester polycarboxylic acid represented by these as an essential component. 2. The compounding amount of the trimellitic acid ester polycarboxylic acid represented by the general formula (1) is 5 times that of the curing agent (B).
The epoxy resin powder coating composition according to claim 1, which is 0% by weight or more.